About Optics & Photonics TopicsOSA Publishing developed the Optics and Photonics Topics to help organize its diverse content more accurately by topic area. This topic browser contains over 2400 terms and is organized in a three-level hierarchy. Read more.

Topics can be refined further in the search results. The Topic facet will reveal the high-level topics associated with the articles returned in the search results.

Abstract

Fiber Bragg Gratings (FBGs) can be used as sensors for strain, temperature and pressure measurements. For this purpose, the ability to determine the Bragg peak wavelength with adequate wavelength resolution and accuracy is essential. However, conventional peak detection techniques, such as the maximum detection algorithm, can yield inaccurate and imprecise results, especially when the Signal to Noise Ratio (SNR) and the wavelength resolution are poor. Other techniques, such as the cross-correlation demodulation algorithm are more precise and accurate but require a considerable higher computational effort. To overcome these problems, we developed a novel fast phase correlation (FPC) peak detection algorithm, which computes the wavelength shift in the reflected spectrum of a FBG sensor. This paper analyzes the performance of the FPC algorithm for different values of the SNR and wavelength resolution. Using simulations and experiments, we compared the FPC with the maximum detection and cross-correlation algorithms. The FPC method demonstrated a detection precision and accuracy comparable with those of cross-correlation demodulation and considerably higher than those obtained with the maximum detection technique. Additionally, FPC showed to be about 50 times faster than the cross-correlation. It is therefore a promising tool for future implementation in real-time systems or in embedded hardware intended for FBG sensor interrogation.

Figures (11)

(a) Normalized reflectivity against wavelength and time under a uniform constant strain C0 = 10−4με. The black line with markers indicates the strain-free spectrum. (b) Theoretical shift of the design wavelength.

Precision of MDA, CCA and FPC algorithms for different wavelength resolutions. The MDA is used in conjunction with a 10 points quadratic interpolation around the maximum. The FPC is as precise as the CCA and considerably more precise than MDA. The peak locking effect is less evident for the FPC than for MDA and CCA.

FBGs reflectivities when no strain is applied. FBG1 and FBG2 are type I gratings while FBG3 is a type II grating. The peak region of FBG3 shows a plateau of about 0.8 nm, increasing the peak detection uncertainty.